It sounds like you've done a lot of research already and are looking for things from farther afield, but last summer at Pinewoods Camp I met Jason Rice and Mark and Sarah Bazeley of the Pixies, who are in your neighborhood, and who carry on the legacy of Bob Cann (Mark's grandfather). Though they're more of a dance band than singers, Jason led a wonderful session on West Country songs, mostly based on a copy of an unpublished manuscript of a memoir-cum-songbook called "Bring Your Guitar" by the late Ken Penney. There were more than 200 songs. They also had a really neat more recent song "in the tradition" called "Craftsmen of the Moor" by Bob Cann. If you need contact info for them, I've got it. (Jason's in Crediton, and the Bazeley's are in Okehampton.)

~ Becky Nankivell (of Cornish antecedants on one side, at least!) in Tucson, Arizona